The present invention relates to an image forming apparatus equipped with a belt for conveying record sheets, and a photosensitive element and a transfer element which are arranged opposite to each other with the belt interposed therebetween.
A conventional electrophotographic image forming apparatus is known, for example, from Japanese Laid-open Patent Application No. 2007-10976. In this type of image forming apparatus, developer is transferred on a record sheet during the conveyance of the record sheet on an endless belt. To be more specific, the belt of this conventional image forming apparatus is looped around a plurality of rollers, and a bridging portion, i.e., a portion whose ends are supported on adjacent rollers with a tension applied to the belt, lies interposed between a photosensitive element and a transfer element. Since the photosensitive element carries developer that is charged in a predetermined polarity and the transfer element is applied with a transfer bias having a polarity that is opposite to the developer, the developer is drawn or transferred from the photosensitive element to the transfer element. When the transfer bias is applied to the transfer element, the inner peripheral surface of the belt is charged in the polarity that is opposite to the transfer bias because of the effect of the transfer bias, whereas the outer peripheral surface of the belt is charged in the same polarity as the transfer bias. Accordingly, the developer is transferred from the photosensitive element toward the belt so that images are formed on a record sheet by the developer.
The object of the present invention is to provide an image forming apparatus which further improves image quality of transferred images on a record sheet.
As a result of intensive search to attain the objective mentioned above, the inventor of the present invention has found that image quality of transferred images can be improved further if the outer peripheral surface of the belt is charged in the polarity that is opposite to the developer before a record sheet reaches the transfer position.